The invention relates to an externally ignited internal combustion engine of the type which includes a main combustion chamber and a separate ignition chamber in which the spark plug is located. The main combustion chamber and the ignition chamber communicate through a channel which terminates in the ignition chamber substantially tangentially.
Due to the presence of the ignition chamber, even very lean fuel-air mixtures can still be ignited in the main combustion chamber. The reason for the favorable ignition properties is due to the fact that, instead of having a single electric spark, such as is present in ordinary internal combustion engines, the ignition in the main combustion chamber is initiated by a torch-like jet which bursts out of the ignition chamber. It is this jet which permits a uniform reaction of the charge even when the mixtures used are very lean. The mixture prevailing in the ignition chamber is ignited in known manner by means of a spark plug. In a known process, the ignition chamber is supplied with a substantially richer mixture than that supplied to the main combustion chamber which, in turn, is created by supplying supplementary fuel. In these so-called "stratified charge" engines, any faulty mixture preparation (for example due to soot deposition in the injection valve) may cause excessive enrichment in the region of the spark plug and thus cause ignition failure or incomplete combustion which, in turn, would lead to a deterioration of the power and the purity of the exhaust gases of the engine. These problems which occur in stratified charge engines are magnified because the tangential influx causes centrifugal forces which have an effect especially on the heavier fuel drops in the fuel-air mixture. The same is true for rotary piston engines although, in rotary piston engines, the main combustion chamber rotates at the same rate as the piston.
In order to counteract these above-mentioned difficulties, it has been proposed in a known internal combustion engine of this type to dispose the spark plug in a separate chamber, immediately adjacent to the ignition chamber, into which the enriched mixture flows from the ignition chamber through channels to be ignited. In this last process, there is a danger of the deposition of soot in the very narrow channels as between ignition chamber and separate chamber. Furthermore, no swirl or vortex is created in the ignition chamber so that the reaction velocity of the charge in the ignition chamber is lower than in a swirl chamber design, which again brings disadvantageous characteristics of the energetic reactions in the main charge.
Furthermore, stratifications of the charge of the type described above entail a substantially increased cost because they require a direct injection system with the corresponding requirement for timing the fuel injection, the ignition and correlating these times with the overall timing of the engine.
Also known are engines with an ignition chamber in which very high compression and a high turbulence of a substantial portion of the total charge is supposed to provide the very maximum power. However, these engines exhibit very rough running and relatively unfavorable exhaust gas characteristics. The high compression in the main combustion chamber results in a high mixture temperature which creates so-called hot cells, i.e, regions of especially elevated temperature, so that, in these locations, there is the possibility of auto-ignition of the fuel-air mixture. By creating a rotational motion in the main combustion chamber, such auto-ignition is counteracted but, again, rotational motion coupled with high compression in the main charge leads to a rough-running engine and, furthermore, such a mixture is harder to ignite because it contains vortices of large diameter. Thus, the ignitability, the exhaust gas requirements, the smooth running of the engine, small dead space, power, fuel consumption, etc., all make certain demands on the design and are of such complicated and partially contradictory nature that an optimum compromise among all these requirements is very difficult.